Sharp shooter
Final sharpening
With pre-sharpening out of the way, editing of a photograph can take place, but sooner or later you are going to want to output the image in some form or another. Generally speaking, lower resolution images, like those destined for online use, require less sharpening than pictures that are to be output at higher resolutions, such as through an inkjet printer. For this reason it is good practice to save images without this final level of sharpening applied. Clients may even request images that are completely unsharpened, so they can take control of this aspect themselves – magazines and image libraries like Alamy are good examples.
So how much sharpening should you apply at the final stage? Well, in the good old days of Unsharp Mask, a good rule of thumb was to set the Radius control to a value equal to the output resolution divided by 200; the Amount to anywhere between 100 and 150; and the Threshold to zero. While this is still good advice, anyone crossing over to Smart Sharpen can be a little more adventurous with the Radius setting, providing that Lens Blur is selected from the drop-down Remove menu. After all, the filter should selectively pick out the edges well enough, and any halos – the most common sharpening artefact – can be eliminated in advanced mode anyway.
It’s useful at this point to stop and ask ourselves a fundamental question: just what is sharpness anyway? What we understand as sharpness is actually an amalgamation of two properties: resolution and acutance. Resolution is something that photographers are familiar with – it’s all about the level information that can be captured in a picture. Resolution is determined by a number of factors, but the most common and important here are pixel count and the ability of a lens to resolve detail.
Acutance is loosely defined as the change in brightness that occurs along an object’s edge. The higher the contrast across this edge, the sharper it will appear. Of these two properties, it is acutance that is affected by filters such as Unsharp Mask and Smart Sharpen. They enhance contrast across an edge and give the impression that everything is sharper. It’s very important to understand that filters like this cannot enhance resolution in any way, that is to say it’s not possible to add detail to a picture where there is none to begin with.
Armed with this understanding of how sharpening works it is possible to bypass Smart Sharpen completely and enhance the acutance in a scene manually. Of course this takes more time, but it can also yield greater control and even be non-destructive, meaning you can save a sharpened file safe in the knowledge you can always undo it.
To do this, the principle is actually very simple: duplicate the layer holding your image, apply a filter that finds edges (traditionally High Pass in the Filter>Render menu) and change the blending mode of this new layer to Overlay to enhance contrast across edges. Now it’s possible to erase this layer where sharpening isn’t required, or just tone it down in places using the Opacity control in the Layers palette.
It’s always important to remember that no two photographs require the same amount of sharpening, and this is why taking control of this much automated (and often much neglected) process can really enhance your photography. Leaving a camera to its own devices may be fine for holiday snaps and enthusiast photography, but in the competitive world of professional photography sharpening is as important as any other part of the digital workflow. Remember folks, the devil is in the detail and, after all, isn’t that what sharpness is all about?
Before and after non-destructive sharpening using the high-pass filter.
Sharpness and Resizing
Staying sharp isn’t always about sharpening filters, there is something to be said for avoiding the problem in the first place. A common source of softness is image resizing, but buried away in the Resize Image dialogue box are a couple of options that can help.
When making images smaller, choose Bicubic Sharper from the drop-down Resample Image menu. And likewise, when making images larger select Bicubic Smoother to remove any artefacts, then follow this with a sharpening step at the end of the workflow.
To see Contact details go to the Directory
